chem 106 test 4 Flashcards
four zones of a weak acid titration and how to calculate
- initial - ICE table for the acid
- before equivalence point - Henderson Hasselbach
- at equivalence point - ICE table b/c all acid has been used up
- after equivalence point - all strong base (weak base is trivial) so do -log[OH-]
how to choose an indicator
changes color a little after the equivalence point
how to write balanced equation for solubility
NaCl (s) -> Na+(aq) + Cl-(aq)
Ksp equation
ex: NaCl (s) -> Na+(aq) + Cl-(aq)
Ksp = [Na+][Cl-]
how to solve for molar solubility
ex: AB2 -> A^2+ + 2B^-
Ksp = (x)(2x)^2
x will give you M
When is a solution saturated? supersaturated?
Q = Ksp -> saturated
Q > Ksp -> supersaturated (some will precipitate out)
ΔG equation we have to have memorized
ΔG = ΔH - TΔS
ΔS = +
more disorder
ΔS = -
more order
S is greater for (gases/liquids/solids)
gas > liquid > solid
disorder -> order
ΔG = -
spontaneous
ΔG = +
nonspontaneous (spontaneous in the opposite direction)
ΔG = 0
equilibrium
ΔH = - (exothermic) and ΔS = + (more disorder)
spontaneous at all temperatures
ΔH = + (endothermic) and ΔS = - (more order)
nonspontaneous at all temperatures
ΔH = - (exothermic) and ΔS = - (more order)
spontaneous at low temperatures
nonspontaneous at high temperatures
ΔH = + (endothermic) and ΔS = + (more disorder)
nonspontaneous at low temperatures
spontaneous at high temperatures
for the Nernst equation ΔG = ΔG* + RTlnQ, a small Q indicates a shift (left/right) and a large Q indicates a shift (left/right)
right - ΔG decreases so more spontaneous; left - ΔG increases so more nonspontaneous
if ΔG* is negative, Keq is
large
if ΔG* is positive, Keq is
small
OIL RIG
oxidation is losing e-s (increase in oxidation number)
reduction is gaining e-s (decrease in oxidation number)
to balance half reactions,
- balance the atoms in each half reaction first
- balance the electrons in each half reaction
- multiply the full equations by the LCM to balance the total number of electrons
oxidation occurs at the ? and reduction occurs at the ?
anode; cathode
AN OX, RED CAT
the cathode (gains/loses) mass
loses - ionizing
the anode (gains/loses) mass
gains - solidifying
positive voltage, electrons flow from
anode to cathode
an Ampere is a
Coulomb/sec
Faraday’s constant is in units of
Coulombs/mol e-
E*cell =
Ered, cathode - Ered, anode
E*cell = +
spontaneous
E*cell = -
nonspontaneous
spontaneous reaction in terms of Ecell, ΔG, and Keq
Ecell +
ΔG -
Keq big
nonspontaneous reaction in terms of Ecell, ΔG, and Keq
Ecell -
ΔG +
Keq small
elements on the top right of the periodic table are strong ? agents
oxidizing (more electronegative means wants to be reduced more)
elements on the bottom left of the periodic table are strong ? agents
reducing (want to be oxidized)
batteries die when
they are at equilibrium; Ecell = 0 V
Electrolysis: if E*cell is a negative voltage,
you can put that many volts into the system to make that reaction occur
work: 1 J =
C * V
kWhr =
3.6 x 10 ^ 6 J
